Police in Norway have detonated an explosive device which was left on a busy commercial street in the centre of Oslo.

A large area was cordoned off following the security alert in the Norwegian capital on Saturday night.

Investigators said the explosive was discovered outside Groenland underground station, and heavily armoured officers swept through the surrounding area to evacuate people from bars and restaurants.

When asked about the controlled explosion, a police spokesman said: "The noise from the blast was louder than our explosives themselves would cause."

Enquiries are continuing at the scene, but detectives believe the explosive was capable of causing only a limited amount of damage.

Image:Norway was put on high alert following Friday's truck attack in neighbouring Sweden

One man has been arrested and is being held in custody, but officers have refused to give any further information about the suspect.

The Groenland area is a multi-ethnic neighbourhood which is home to several popular bars and restaurants. Oslo's main police station lies less than a kilometre away from where the explosive device was found.

Malin Myrvold, who saw the police activity unfold from the fourth floor of a nearby building, said: "Every restaurant was being closed. You could see cops in heavy armour going in every store and restaurant.